1. Field of the Invention
Radiation sensitive compounds which addition polymerize rapidly in the presence of actinic or ionizing radiation are of interest for use in film-forming compositions. Of particular interest are fast-curing compounds which provide elastomeric and wearlayer films having improved durability and flexibility.
2. Description of the Prior Art
Film-forming compositions containing radiation curable components are well-known. Films formed from compounds having urethane moieties and acrylate functional groups are recognized to possess very good wear and weather resistance properties and also have good flexural strength properties. Typical of these urethane-acrylate radiation-curable film-forming materials are the compositions disclosed in U.S. Pat. No. 3,509,234 to Burlant et al and No. 4,038,257 to Suzuki et al. Although these urethane acrylate compositions have gained widespread acceptance for forming protective and decorative films on a variety of substrates, there is ever increasing demand for compositions which cure quickly to form tough, flexible films. The advantages of shorter curing times include productivity increases coupled with potential savings in energy consumption. Moreover, a composition which cures quickly after application to a substrate is likely to form a cured coating of higher gloss and smoothness inasmuch as the wet film is exposed for a lesser period of time to contamination from dust-laden environments typically attending coating operations.
Coating compositions containing very fast curing components have been devised. For example, copending U.S. application Ser. No. 821,856, filed Aug. 7, 1977, of G. W. Gruber, discloses coating compositions containing amide moieties and acrylate functional groups that can form very hard films on coated substrates passing under a curing radiation source at about 350 feet per minute. These amide acrylate compounds do not, however, provide cured films having particularly good flexural strength properties.
Fast-curing compositions for forming tough, flexible protective or decorative films would be quite useful for coating floor tile, vinyl overlays used in covering furniture and other articles, and various other flexible substrates. Baseboard coving, for example, is typically made of rubber or flexible plastic materials which require protective films of good flexibility since the coving materials are frequently shipped in rolls and are folded or bent during application to a wall base. Vinyl overlay coverings, often only two to ten thousandths of an inch in thickness, are frequently used to cover furniture and other articles having sharp-angled surface configurations. Protective films for these vinyl coverings must have sufficient flexural and tensile strength properties to withstand folding and creasing without the film cracking, tearing or lifting from the vinyl substrate.
A class of addition polymerizable or radiation-curable compounds characterized in having a molecule comprising amide and urethane moieties, and an ethylenically unsaturated functional group such as an acrylate functional group, is disclosed in copending U.S. Application Ser. No. 890,895 of C. B. Friedlander et al, filed on even date herewith, now U.S. Pat. No. 4,153,776, issued May 8, 1979. This class of addition polymerizable amide urethane acrylate compounds comprises the addition reaction products of an amide compound containing at least one hydroxy functional group, a polyisocyanate and a polyfunctional compound containing at least one hydroxy functional group reactive with an isocyanato group of the polyisocyanate and which polyfunctional compound provides at least one ethylenically unsaturated functional group in the reaction product.
Films formed from compounds of the aforementioned class of amide urethane acrylate compounds possess improved abrasion resistance and tensile strength as compared to films made from urethane acrylate compounds; moreover, compositions containing the amide urethane acrylate compounds addition polymerize in the presence of radiation relatively quickly. This combination of properties makes amide urethane acrylate compounds especially useful as radiation-curable coatings for floor tile and wall-base coving.